This application for a Mentored Patient-Oriented Research Career Development Award (K23) is an initial submission by a new investigator. The candidate proposes a program of research and training with the following goals: 1) to further his understanding of obesity;2) to expand his knowledge of clinical nutrition and type 2 diabetes;and 3) to acquire clinical research skills that will prepare him for a career as an independent investigator. This training will allow the candidate to conduct a randomized controlled trial that will compare different dietary interventions for facilitating weight and glycemic control in individuals with type 2 diabetes. Overweight and obese persons with type 2 diabetes (n=120) will be randomly assigned to a diet based on the Food Guide Pyramid (FGP) or a low-glycemic index (Gl) diet. The latter emphasizes selecting foods less rapidly converted to glucose. Short-term studies show better-controlled metabolic responses and less ad libitum intake following a low-GI versus isocaloric high-GI meals. Long-term comparisons are needed. The proposed research has two specific aims. The first is to assess the effects of the FGP and low-GI diets on long-term weight control. Weight loss is not expected to differ between groups after 40 weeks of treatment, but patients who receive the low-GI diet are predicted to maintain greater reductions at follow-up (weeks 66 and 92). Changes in glycemic control and cardiovascular risk factors are similarly expected to be superior with the low-GI diet at follow-up. Exploratory analyses will compare long-term changes in hunger, body composition, and resting energy expenditure. The proposed study will be the first long-term trial to assess the effects of consuming a self-selected low-GI diet in adults with type 2 diabetes who are attempting to lose weight with a program of diet, exercise, and behavior therapy. The research and training experiences described in this proposal will prepare the candidate for continued independent clinical research in the field of obesity and related disorders.